According to portable engine-driven tools, such as a bush cutter and a chain saw, a worker often works while tilting such an engine-driven tool in various directions. Accordingly, it is requisite for an engine to stably operate even in the tilted condition. In particular, according to four-cycle engines, the interior of an engine is lubricated by supplying oil in an oil tank provided in the engine to individual parts of the engine. Consequently, it is necessary to supply the oil to the interior of the engine even if the engine is in a tilted condition. Accordingly, for example, a technology of Patent Literature 1 employs a structure which has an oil room in a crankcase separately from a crank room and which prevents the oil in the oil room from flowing back into the crank room.